1. Field of the Invention
The present invention relates to a special kind of postcard with a part thereof invisible, more particularly to a postcard secret information is kept covered during mailing and the recipient can see it at his own discretion, and a method of manufacturing it.
2. Description of the Prior Art
Recently, mail containing secret information such as the balance of a person's bank deposit has been increasing. It has, therefore, been desired to develop a postcard, a part of which containing secret information is kept covered during mailing, but which the recipient can see without difficulty. Japanese Utility Model Publication No. 3789/'79 discloses a post card, of which a part, for instance, a marked part is kept covered until it is uncovered by the recipient to see the secret information hidden thereunder.
To make it partly viewable, however, as seen from the text of the aforementioned Japanese Utility Model Publication No. 3789/'79, the entire surface of a covering paper has to be coated with a drying paste to form an adhesive film and the postcard material is partly, for instance, coated with a silicone release agent or the like so that the covering paper can be partly removed. Thus, since the covering paper has to be coated with a drying paste and the postcard material has to be partly treated with a release agent such as one based on silicone, the construction of such postcard becomes inevitably complicated and the increased number of manufacturing steps results in an increased manufacturing cost.